Video coding technologies are widely used in the communications field. Digital video contents exist in coded form for saving storage. Coding includes MPEG-2 technology defined by the Moving Picture Experts Group (MPEG), for example. Transcoding coded video contents from one format to another, from one bit rate to another and from one resolution to another are indispensable in many multimedia applications. Multimedia applications include, for example, digital video broadcasting, video on demand (VOD), teleconferencing, long distance learning, and so on.
One approach involves transcoding into an H.264 sequence with arbitrary spatial resolution out of an MPEG-2 main profile sequence. This approach reuses parameters of a source MPEG-2 macroblock into an H.264 macroblock based on a one-to-one mapping. A second approach involves producing one motion vector per macroblock of the target resolution by using motion vectors of the source picture so only a 16×16 partition is generated for new target macroblocks. This approach cannot exploit the compression efficiency tool of supporting smaller partitions.
A third approach involves MPEG-2H.264 transcoding with down sampling that exploits variable block-size motion estimation features of H.264. The resolution change permitted is only half the spatial resolution, and it is not meant for an arbitrary resolution change. A fourth approach involves video transcoding with variable block-sized motion estimation, which is a top-down approach. Partitioned motion vectors are determined based on the determined motion vector of the 16×16 partitions. A fifth approach involves an arbitrary video downsizing in which the motion vector determination logic is based on an area-weighted-median vector.
All the candidates for macroblock partition mode selection are not always considered. Instead, the dominant partition for combination has the most influence. A sixth approach involves an H.264-H.264 arbitrary resolution change. This approach utilizes the additional information available in H.264 data as compared with MPEG2, and does not completely avoid motion-estimation. It uses a search window having a size 2 to 6. This approach uses the strategy of making the smallest partition's motion vector first (bottom-up approach), then continues to merge the smaller partitions into larger ones up to a 16×16 partition (mode refinement strategy) as determined by some of the conditions. Hence, this reduces the efficiency since such a strategy has computational complexity.